The present invention relates to a magnetic head for reproducing information recorded at high density and a method of producing the magnetic head, and a magnetic recording and reproducing apparatus comprising the magnetic head, as well as a perpendicular magnetic recording medium, such as a video disc or a hard disk, and a method of producing the medium.
A magnetic recording and reproducing apparatus is available in various types, such as a tape recorder, a video tape recorder and a magnetic disc apparatus. The magnetic recording and reproducing apparatus is evolving so as to carry out high-density recording and have been improved in many ways to achieve the purpose. These improvements are: a track is made narrower by using a narrower head; a plurality of magnetic heads are used; a recording medium is made smoother and thinner; the relative speed between the magnetic head and the recording medium is increased; and so on.
Accordingly, there is a need for a magnetic head capable of recording information on a magnetic recording medium at high density and also capable of reproducing the information. To meet such a need, a complex MR head comprising an MR (magneto-resistance) head, which is a reproduction-only head having a higher reproduction sensitivity than that of a widely used induction type head, has become commercially available. The complex MR head is provided with both the MR head and a conventional induction thin-film head. The MR head having high reproduction sensitivity is used in reproduction, and the conventional induction thin film head is used in recording. The MR head comprises a magneto-resistance effect device (hereinafter referred to as an MR device). However, the structure of the complex MR head comprising the MR device is more complicated than that of a conventional induction head. More specifically, a shielding layer is required around the MR device, and a magnetic gap is required for reproduction. Furthermore, it is necessary to have a structure for arranging an MR film so that the MR film can have a single magnetic domain, and it is also necessary to have a unique structure for applying a bias magnetic field for linear reproduction.
For these reasons, advanced production technology is required for producing the complex MR head, thereby making it difficult to attain high yield.
Longitudinal recording, wherein magnetization is performed in the direction parallel to the track of a recording medium, has been used as a recording method for a conventional magnetic recording and reproducing apparatus. However, in the case of the longitudinal recording, micro magnetic domains magnetized in the direction parallel to the surface of a recording film repels adjacent magnetic domains, and they tend to mutually weaken magnetization. This tendency becomes more significant as recording density is higher, thereby causing a limitation in high-density recording.
Perpendicular magnetic recording, wherein magnetization is performed in the direction perpendicular to the surface of a recording medium, is available as a method of solving the above-mentioned problem. A perpendicular magnetic recording median having a two-layer structure has been commercially available as a recording medium for performing recording in accordance with perpendicular magnetic recording. In the perpendicular magnetic recording medium, a soft magnetic film having a high permeability is used as a foundation layer. A perpendicular recording film having an axis of easy magnetization in the direction perpendicular to the surface of the soft magnetic film is laminated on the foundation layer. The soft magnetic film is made of a nickel-iron alloy (Nixe2x80x94Fe) or the like, and the perpendicular recording film is made of a cobalt-chromium alloy (Coxe2x80x94Cr) or the like. These films are formed by sputtering or the like. When these films are formed, it is desired that the soft magnetic film and the perpendicular recording film are continuously formed in a vacuum chamber so as to prevent contamination caused by entry of dust or by formation of oxidized films between the soft magnetic film used as the foundation layer and the perpendicular recording film. In this case, the sputtering process is conducted while the substrate of a recording medium passes over two kinds of target materials in sequence at a predetermined speed.
The soft magnetic film, namely, the foundation layer, allows the recording magnetic field from the perpendicular magnetic head for perpendicularly magnetizing the perpendicular recording film to pass in the longitudinal direction parallel to the surface of the recording medium and to return to the perpendicular magnetic head. In addition, the soft magnetic film has a role to enhance the efficiency of magnetic field generation in record and reproduction. Therefore, controlling the anisotropy of the soft magnetic film is important to enhance record and reproduction characteristics. In other words, it is necessary to align the axis of hard magnetization, which is orthogonal to the axis of easy magnetization of the soft magnetic film, in the traveling direction of the substrate in record and reproduction. In the case of a magnetic disc, it is necessary to align the axis of hard magnetization of the soft magnetic film in the direction parallel to the circumference of the disc, since a recording track is formed in the direction along the circumference thereof.
A method of forming a soft magnetic film by controlling the angle between the target material and the substrate and a method of forming a soft magnetic film by applying a magnetic field have been proposed as control methods of the anisotropy of the soft magnetic film. Furthermore, a method of applying a magnetic field after the soft magnetic film was formed and before the perpendicular recording film is formed has also been proposed (Japanese Laid-open Patent Application Hei 5-258274). A method of applying a magnetic field in the radial direction of the magnetic disc has been proposed as a method of aligning the axis of hard magnetization of the soft magnetic film in the direction parallel to the circumference of the magnetic disc. In all these methods, processing is carried out before or while the perpendicular recording film is formed.
When a magnetic field is applied to a perpendicular magnetic recording medium in a vacuum, difficult problems are caused in handling; for example, a complicated mechanism must be provided and operated in a vacuum sputtering apparatus. For easier handling, it is desired that a magnetic field is applied by using an apparatus which is separate from the sputtering apparatus and provided in the atmosphere. However, since it is desired that the soft magnetic film and the perpendicular recording film are continuously formed in a vacuum as described above, sputtering is performed by passing the substrate over two target materials in a vacuum at a predetermined speed.
In a currently available sputtering apparatus, however, in order to apply the magnetic field to the magnetic disc in the radius direction before forming of the perpendicular recording film, the sputtering process must be interrupted once after the soft magnetic film is formed, and the perpendicular magnetic recording medium must be taken out to the atmosphere. In case the continuity of the film forming process is lost as described above, there is the danger of contaminating the recording medium because of entry of dust or formation of oxidized films between the foundation layer and the perpendicular recording film. Besides, sputtering must be performed twice for the foundation layer and the perpendicular recording film layer, thereby increasing the number of steps, lowering productivity, and increasing production cost.
Other problems encountered in high-density record and reproduction are caused by tracking control methods. According to one of the methods, in order to perform tracking control for a predetermined track of a magnetic disc, markers are formed on the recording medium by a physical process using etching or the like, and servo control is activated by using laser beams reflected from the markers. As a method of placing the markers, pits and projections are formed by processing the surface of the medium by a physical process such as photolithography or the like. However, this method causes high production cost. Furthermore, in the case that the method is used for hard disk drives (HDD), the floating condition of the head is changed by the pits and projections in high-density recording, and the head might be damaged in an extraordinary case.
Accordingly, an object of the present invention is to provide a magnetic head being relatively simple in structure and superior to a conventional induction head in reproduction sensitivity, a method of producing the magnetic head, and a magnetic recording and reproducing apparatus comprising the magnetic head.
Another object of the present invention is to provide a method of properly producing a perpendicular magnetic recording medium superior in record and reproduction characteristics by taking fewer number of steps. This can be achieved by generating longitudinal magnetic anisotropy in the low coercive force layer of a foundation layer via the application of heat and a magnetic field after formation of a perpendicular recording film, and by aligning the axis of hard magnetization of the low coercive force layer in the traveling direction of a substrate in record and reproduction.
Furthermore, in a perpendicular magnetic recording medium comprising a transparent nonmagnetic substrate and a low coercive force layer of amorphous, soft magnetic portions are made nonmagnetic when portions of the amorphous layer are crystallized by applying a laser beam from the nonmagnetic substrate after formation of the magnetic recording layer. As a result, the nonmagnetic portion has a characteristic close to that of a single layer film, and a perpendicular magnetic recording medium capable of distinguishing between a signal recorded portion and a servo signal detection portion can be obtained without losing the smoothness of the surface. A still another object of the present invention is to provide a magnetic recording and reproducing apparatus which uses the above-mentioned magnetic recording medium.
In order to achieve the above-mentioned objects, the magnetic head of the present invention comprises a first magnetic core and a second magnetic core, each comprising a soft magnetic film and one end of each facing a magnetic recording medium; a third magnetic core disposed between the first and second magnetic cores, magnetically connected to the other ends of the first and second magnetic cores, and having a thickness smaller than the first and second magnetic cores; a conductive wire passing through the third magnetic core while being insulated from the third magnetic core; and a conductive coil wound around the third magnetic core.
The magnetic head of the present invention is configured so as to arrange the conductive wire passing through the third magnetic core while being insulated from the third magnetic core to a perpendicular head of a main magnetic pole exciting type including auxiliary magnetic poles having the first and second magnetic films, a main magnetic pole having the third magnetic core and a coil for generating record signal magnetic field. Therefore, the magnetic head has a structure capable of performing perpendicular magnetic recording, thereby being capable of performing record and reproduction at higher density. Moreover, since the conductive wire is disposed so as to pass through the third core while being insulated from the third magnetic core, the third magnetic core is used as a magnetic impedance element. This makes it possible to perform reproduction which uses a magnetic impedance effect and is higher in sensitivity than that in reproduction attained by conventional heads.
In addition, since the head of the present invention is a magnetic flux responsive type similar to the MR head, the head can meet the need for reduction in the moving speed of a magnetic recording medium because of miniaturization of recording and reproducing apparatuses.
The third magnetic core comprises first and second soft magnetic films, and the area of an end surface of each of the first and second soft magnetic films, facing the magnetic recording medium, is smaller than the area of the other end surface. As a result, the magnetic flux density at the end surface facing the magnetic recording medium becomes higher, and the intensity of recording magnetization increases.
Since the third magnetic core comprises the first and second soft magnetic films, the magnetic head can be produced by using the pattern forming method.
The method of producing the magnetic head of the present invention comprises a step of forming the first soft magnetic layer, a step of forming a first insulation layer on the first soft magnetic layer, a step of pattern forming first conductive layers on the first insulation layer, a step of forming a second insulation layer on the conductive layers, a step of forming the second soft magnetic layer on the second insulation layer, a step of forming a second conductive layer of line-shape for a conductive wire on the second soft magnetic layer, a step for forming a third soft magnetic layer on the second soft magnetic layer so as to put the second conductive layer between the second and third soft magnetic layers, a step of forming a third insulation layer on the third soft magnetic layer, a step of forming third conductive layers on the third insulation layer so as to compose of a conductive coil by connecting with the first conductive layers, a step of forming a fourth insulation layer on the third conductive layers, and a step of forming a fourth soft magnetic layer on the fourth insulation layer.
Since the conductive layer can be formed by the pattern formation method, the magnetic head can be produced easily.
The magnetic recording and reproducing apparatus of the present invention uses the above-mentioned magnetic head, and is provided with carrier signal application means for applying to the conductive wire a high-frequency signal having a constant current on which a DC current for a bias magnetic field is superimposed.
Since recorded information is reproduced on the basis of a high-frequency voltage detected by a magnetic field obtained by a bias magnetic field superimposed on an external magnetic field, the reproduction sensitivity of the head is higher than that of a conventional induction head.
Furthermore, the reproduction means comprises a high-frequency voltage detection portion for detecting a high-frequency voltage generated across the conductive wire and changed on the basis of the high-frequency signal having the constant current depending on a magnetic field obtained by the bias magnetic field superimposed on an external magnetic field caused by the magnetic recording medium, and an AM demodulation portion for amplitude-demodulating a detected high-frequency voltage.
The recorded information can be reproduced easily by AM-demodulating the detected high-frequency voltage.
A perpendicular recording medium of the present invention is obtained by sequentially forming a low coercive force magnetic layer of a magnetic thin film and a perpendicular magnetic recording layer having an axis of easy magnetization in the direction perpendicular to the recording layer on a nonmagnetic substrate. By applying heat and a magnetic field after the formation of the perpendicular magnetic recording layer, longitudinal magnetic anisotropy is generated in the low coercive force magnetic layer, and the axis of hard magnetization is aligned in the traveling direction of the substrate in record and reproduction.
By applying a magnetic field while heating the low coercive force magnetic layer to a predetermined temperature after the formation of the low coercive force magnetic layer and the perpendicular magnetic recording layer, longitudinal magnetic anisotropy is generated on the soft magnetic film. The axis of hard magnetization is thus aligned in the traveling direction of the substrate in record and reproduction. Consequently, the permeability of the low coercive force magnetic layer increases in the traveling direction of the substrate. Therefore, the intensity of the magnetic field increases during recording wherein a magnetic field is generated in the same direction as the traveling direction of the substrate. This increases the intensity of the residual magnetic field of the perpendicular magnetic recording layer, and raises the output level of a reproduction signal.
The perpendicular magnetic recording medium of the present invention is produced as described below. A circular plate used as a jig on which a perpendicular magnetic recording medium is placed is heated, and the temperature thereof is detected and controlled so as to have a constant value. While a magnetic field is applied by using a magnet in the radial direction of the perpendicular recording medium, the circular plate is rotated so that longitudinal magnetic anisotropy is generated at the low coercive force magnetic layer. In other words, after the formation of the soft magnetic film and the perpendicular recording film of the perpendicular magnetic recording medium, a magnetic field is applied to the soft magnetic film while the film is heated to a predetermined temperature in the atmosphere. As a result, longitudinal magnetic anisotropy is generated at the soft magnetic film, and the axis of hard magnetization thereof is aligned to the traveling direction of the substrate in record and reproduction. Consequently, the method can be conducted more easily than a conventional method of applying a magnetic field in a vacuum. Since the soft magnetic film and the perpendicular recording film are continuously formed by sputtering, the perpendicular magnetic recording medium can be obtained at higher productivity and a lower cost.
Furthermore, a low coercive force magnetic layer having an amorphous magnetic thin film, and a perpendicular magnetic recording layer having an axis of easy magnetization in the direction perpendicular to the surface thereof are sequentially formed on the nonmagnetic substrate of the perpendicular magnetic recording medium. Portions of the amorphous film are then crystallized. In other words, by forming the low coercive force magnetic layer of the perpendicular magnetic recording medium from an amorphous material, and by applying a laser beam to portions of the layer so as to crystallize the portions, the portions can be used as markers for servo control.
Furthermore, in the perpendicular magnetic recording medium, the low coercive force magnetic layer comprising the amorphous magnetic thin film is made of an amorphous alloy (Coxe2x80x94Zrxe2x80x94Ta) containing cobalt, zirconium and tantalum.
The record and reproduction characteristics of the head can be improved by using the soft magnetic film made of the amorphous Coxe2x80x94Zrxe2x80x94Ta material.
In the perpendicular magnetic recording medium, the crystallized portions of the low coercive force magnetic layer comprising the amorphous material are used for plural kinds of servo control.
In particular, the crystallized portions of the amorphous soft magnetic film of the perpendicular magnetic recording medium are used for servo control. Since the crystallized portions have no pits or projections, the surface of the disc can be maintained smooth.
In the method of producing the perpendicular magnetic recording medium in accordance with the present invention, a thin film magnetic recording layer of low coercive force made of an amorphous material, and a perpendicular magnetic recording layer having an axis of easy magnetization in the direction perpendicular to the surface of the layer are sequentially formed first on a nonmagnetic transparent substrate. After the magnetic recording layer is formed, a laser beam is applied for the nonmagnetic substrate so as to crystallize portions of the thin film magnetic recording layer made of an amorphous material.
Since a laser beam is applied to the side of the nonmagnetic substrate after providing the amorphous low coercive force magnetic layer and the perpendicular magnetic recording layer on the nonmagnetic transparent substrate, the perpendicular magnetic recording medium having desired crystallized portions in the amorphous film can be produced without losing the continuity in the sputtering process of producing the amorphous film and the perpendicular recording film.
The magnetic head of the present invention comprises magnetic cores and a magnetic yoke, each including a soft magnetic thin film, and the magnetic cores and the magnetic yoke form a closed magnetic circuit via the above-mentioned perpendicular magnetic recording medium. In addition, the magnetic head has a second winding for recording and reproducing signals, and another winding for causing a change in impedance and detecting the change.
Furthermore, the magnetic head has a winding for recording and reproducing signals, and another winding for detecting a change in impedance so as to accurately control the position of the head.
The magnetic recording and reproducing apparatus of the present invention comprises the above-mentioned magnetic head moving relative to the above-mentioned perpendicular magnetic recording medium so as to record and reproduce signals, drive means for moving the magnetic head in the horizontal direction along the surface of the magnetic recording medium, drive means for moving the magnetic head in the direction perpendicular to the magnetic head so as to finely adjust the distance between the magnetic recording medium and the magnetic head, record signal supplying means for supplying record signals to the magnetic head, and means for detecting noncrystallized portions and crystallized portions of the amorphous layer of the magnetic recording medium depending on a change in impedance of the winding of the magnetic head at the time of application of a high-frequency voltage to the winding, and control drive means for detecting the change in the impedance of the winding and for tracking the magnetic head so that the detection signal level corresponding to the impedance value becomes maximum.
The magnetic recording and reproducing apparatus comprises means for detecting noncrystallized portions and crystallized portions of the amorphous layer of the medium by detecting a change in the impedance of the winding during reproduction, and control drive means for tracking the magnetic head along a locus where signals have been recorded so that the level of the detection signal becomes maximum.
The noncrystallized portions and crystallized portions of the amorphous soft magnetic layer are detected as a change in the impedance of the winding of the head, and servo control is carried out depending on a change in output voltage on the basis of the change in impedance. As a result, tracking can be carried out accurately.
During reproduction, the noncrystallized portions and crystallized portions of the amorphous layer are detected as a change in the impedance of the winding of the head, and the head is controlled so that the detected reproduction output is as high as possible, whereby tracking can be carried out highly accurately.
In the production of the perpendicular magnetic recording medium of the present invention, the sputtering process for the low coercive force magnetic layer used as a foundation layer and the sputtering process for the perpendicular magnetic recording layer are carried out continuously. After the formation of the perpendicular magnetic recording layer, heat and a magnetic field are applied so as to generate longitudinal magnetic anisotropy at the low coercive force magnetic layer. The axis of hard magnetization is aligned in the traveling direction of the substrate in record and reproduction. Consequently, it is possible to provide a magnetic recording medium having proper record and reproduction characteristics.
The magnetic recording apparatus of the present invention uses a magnetic recording medium wherein a low coercive force magnetic layer comprising an amorphous magnetic thin film and a perpendicular magnetic recording layer having an axis of easy magnetization in the direction perpendicular to the surface of the film are formed in this sequence on a nonmagnetic substrate. A laser beam is applied to portions of the amorphous layer so as to heat and crystallize the portions so that the layer becomes a nearly single layer film comprising only the perpendicular magnetic recording layer while the smooth surface of the disc is maintained. During recording, a tracking signal can be detected by detecting the crystallized portions and the amorphous portions which has not been irradiated with the laser beam.